PURPOSE: To produce carbodihydrazide by reacting urea with hydrazine hydrate, separating and recovering the subject high-quality compound from the solution mixture, recycling a part of the mother liquor into the reaction system and recovering and re-utilizing the hydrazine hydrate from the remaining mother liquor.

CONSTITUTION: Urea is reacted with hydrazine hydrate in a molar ration of 1:3 to 1:10 at 120-190°C. The reaction mixture containing the produced carbodihydrazide is cooled at 0-20°C in a state of the coexistence of semicarbazide as a reaction intermediate at 0-20°C to crystallize and separate the subject compound. A part of the recovered mother liquor containing the semicarbazide is separated for recylcing for the next reaction, and the hydrazine hydrate is recovered by distilling the remaining recovered mother liquor and again utilized. The carbodihydrazide is useful as a deoxidizer for boilers, and the reutilization of the reaction mother liquor permits to enhance the rate of the reaction and economically utilize the raw materials to be used for the reaction.